The present invention relates to a process for preparing a catalyst support for (stereospecific) polymerization of alpha-olefins, in particular propylene, and to the support thus obtained.
Alpha-olefin polymerization in general is carried out using Ziegler-Natta type catalysts. The Ziegler-Natta type catalyst system is generally constituted by two non-dissociable elements: a transition metal-based catalytic component deposited on a magnesium chloride-based support and a co-catalyst generally based on an aluminum compound. Numerous patents describe these catalyst components and their supports.
European patent application EP-A-0,239,475 discloses a controlled morphology catalyst spherical support for alpha-olefin polymerization. The catalyst support is obtained by reacting a chlorine-containing organic compound in the presence of an electron donor and a prior mixture of an alkylmagnesien and an aluminoxane and/or aluminosiloxane and, optionally, an electron donor. The support is then subjected to an activation step using a chlorine-containing compound prior to impregnation by a transition metal halide. This process leads to effective catalysts for ethylene polymerization. They have however proved to be less effective in particular for polymerization of propylene.
Activation of catalyst supports by treatment with cyclic monoethers for ethylene polymerization catalysts is known. European patent application 0,554,141 discloses, for example, a process for activating a magnesium chloride-based support that enters into the manufacture of the ethylene catalytic polymerization component. This process comprises activating the support in suspension in an inert liquid using a cyclic mono-ether. That patent does nevertheless not disclose nor suggest the possibility of such activation for controlled morphology catalyst supports adapted to propylene polymerization.
U.S. Pat. No. 3,642,746 discloses a Ziegler-Natta catalyst system useful to reduce the ash content of the obtained polymer. The catalyst is prepared by pretreatment of a divalent metal dihalide with en electron donor and impregnation of the obtained support with a transition metal halide.
A process for polymerization of ethylene in the gas phase leading to a linear polyethylene with a narrow weight distribution is known from U.S. Pat. No. 5,055,535. This process uses a Ziegler-Natta catalyst in presence of an alkylaluminium and a monoether. According to this document, the monoether should not be in contact with the catalyst in absence of the cocatalyst in the medium. The monoether constitues therefore an external Lewis Base and intervenes only during the polymerization. Further the monoether does not act as a polymerization activator and does therefore not allow to enhance productivity.
It is known that stereospecific polymerization of xcex1-olefins beyond ethylene such as propylene requires a stereospecific type catalyst. Indeed, contrary to polymerization of ethylene, which is a symmetrical molecule, the polymerization of an asymmetric xcex1-olefin, such as propylene, can lead to isotactic, syndiotactic or atactic chaining. The use of a stereospecific catalyst can then ensure that polymers of the desired structure, such as predominantly syndiotactic or isotactic, for example, are obtained. This explains why catalysts employed for ethylene polymerization are not necessarily suitable for polymerizing polypropylene.
It has now been surprisingly found that activation adapted to ethylene can be applied to a support adapted to propylene.
The invention makes it possible to obtain catalysts which are both highly effective and highly stereospecific for the polymerization of xcex1-olefins with at least 3 carbon atoms, in particular propylene.
The invention consequently provides a process for preparing a catalyst support for polymerizing xcex1-olefins comprising the steps of:
(i) reacting, in the presence of a first electron donor, a chlorine-containing organic compound and a prior mixture of an alkylmagnesien and an aluminoxane and/or aluminosiloxane and/or alkylaluminum and, optionally, a second electron donor; and
(ii) activating the product from step (i) in suspension in an inert liquid by means of an activation electron donor.
The invention also provides a catalyst support obtainable by the process according to the invention.
The invention will now be described in more detail below.
According to the invention, the spherical catalyst support is prepared by reacting, in the presence of an electron donor, a chlorine-containing organic compound with a prior mixture of an alkylmagnesien and an organic compound of aluminium, aluminoxane and/or aluminosiloxane and/or alkyl-aluminum. The chlorine containing organic compound is caused to react in the prior mixture of alkylmagnesien and organic compound of aluminium, the reaction taking place in the presence of a first electron donor. The prior mixture of alkyl magnesien and organic compound of aluminium can also comprise a second electron donor, which, generally, (but not necessarily) is of the same type as the first electron donor.
The reaction is carried out in the presence of a donor, which can be introduced:
through previous mixing of the chlorine-containing organic compound with this (first) donor, or
through previous mixing of the alkylmagnesien and aluminium organic compound (aluminoxane and/or aluminosiloxane and/or alkylaluminum) in this (first) donor; or
both through previous mixing of the chlorine-containing organic compound in this (first) donor and previous mixing of the alkylmagnesien and organic compound of aluminium (aluminoxane and/or aluminosiloxane and/or alkylaluminum) in this (second) donor. In this case, the second donor can be identical to or different from the first donor; it is preferably identical.
According to one embodiment, the chlorine-containing organic compound is mixed with at least a portion of the first electron donor prior to the reaction of step (i), this portion being preferably at least 50%.
According to one embodiment, the amount of first electron donor mixed with the chlorine-containing organic compound prior to the reaction of step (i) represents, in moles, more than 50% of the total of the first and second electron donors present during the reaction of step (i).
In a further embodiment, the reaction of step (i) takes place in the presence of a first electron donor, the prior mixture of an alkylmagnesien and an aluminoxane and/or aluminosiloxane and/or alkylaluminum comprising a second electron donor, identical to the first electron donor.
At the end of step (i), the solid obtained is generally substantially spherical.
The alkylmagnesien is previously mixed with the aluminoxane and/or aluminosiloxane and/alkylaluminium, preferably in solution in an inert solvent such as a hydrocarbon, for example hexane or heptane, preferably in the presence of an electron donor, which can be the first or second donor depending on the case. Once the mixture has been made, the chlorine-containing organic compound, generally (but not necessarily) diluted in a (first) electron donor and optionally in an inert solvent such as hydrocarbon like hexane or heptane is made to react. At the end of the reaction, the support formed, in suspension in the reaction medium, is filtered and optionally washed with inert liquid. The support, in suspension in an inert solvent such as a hydrocarbon like hexane or heptane, is then brought into contact with a so-called activation electron donor, preferably a cyclic ether. This activation operation can be carried out before or after the preceding filtration and washing operations. The support formed is filtered and optionally washed with an inert liquid if the cyclic ether treatment took place after the first filtration and first washing operations. One thus obtains a support the particle diameter of which is generally comprised between 5 and 150 microns and more generally between 10 and 100. The supports and, consequently the subsequent catalysts have a very narrow granulometric distribution width, in general less than 5. The granulometric distribution width of the final polymers is also narrow given that the polymerization process generally does not generate fines, in other words does not damage the growing particle during polymerization. This granulometric distribution width is characterized by span measurement where the span is equal to (D90xe2x88x92D10)/D50 wherein D90, D10 and D50 represent the diameter below which respectively 90%, 10% and 50% by weight of the particles is respectively found. The final polymers generally have a span value less than 5 preferably less than 2.
The alkylmagnesien implemented corresponds to the formula RlMgR2 wherein R1 and R2 are alkyl radicals having 1 to 12 carbon atoms.
The aluminoxane which may enter into the composition of the support is selected from products having the formula: 
wherein Rxe2x80x2 is an alkyl radical having 1 to 16 carbon atoms, the Rxe2x80x3s forming together an O-radical or each representing an Rxe2x80x2 radical and n is an integer from 0 to 20.
The aluminosiloxane which may enter into the composition of the support is selected from products having the formula: 
wherein R1, R2, R3, R4, R5 which may be identical or different, represent an alkyl radical having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms or yet again a hydrogen atom, preferably under the proviso that there are not more than three hydrogen atoms per mole of derivative, or finally a chlorine atom, preferably under the proviso that there are not more than three chlorine atoms per mole of derivative.
The alkylaluminium which may enter into the support composition is selected from products having the formula A1R1R2R3 wherein the groups R1, R2 and R3 have the same definition as above.
The chlorine-containing organic compound, acting as a chlorinating agent for the alkylmagnesien derivative and aluminum organic compound is selected from alkyl chlorides wherein the alkyl radical is primary, secondary or tertiary and optionally comprises a heteroatom, said radical comprising up to 12 carbon atoms, preferably up to 7 carbon atoms among the alkyl polyhalides or among the acid chlorides. Preferred compounds are tertiobutyle chloride, n-butyl chloride, dichloroethane, thionyl chloride, benzoyl chloride.
The reaction is carried out in the presence of a first electron donor and optionally a second donor introduced by the prior mixing of an alkylmagnesien and an aluminum organic compound.
These first and second electron donors that may be identical or different can be selected from the aliphatic or cyclic monoethers and aliphatic or cyclic diethers, aromatic or aliphatic carboxylic acids and their alkyl esters, ketones, vinyl esters, acrylic derivatives, in particular alkyl acrylate or methacrylate, and the silanes. The esters can also be employed in the form of addition products with Lewis acid halides different from the dihalides of magnesium. Particularly suited as first and second electron donors are compounds such as methyl paratoluate, ethyl benzoate, ethyl acetate or butyl acetate, ethylether, ethyl para-anisate, dibutylphtalate, dioctylphtalate, diisobutylphtalate, acetone, methylisobuthylketone, vinyl acetate, methyl methacrylate, phenyltriethoxysilane, cyclohexylmethyl-dimethoxysilane, dicyclopentyldimethoxysilane, 2,2-diisobutyl-1,3-dimethoxypropane. 2,2-diisobutyl-1,3-diethoxypropane, 2-isopropyl-2-isobutyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclohexyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane, 2,2-dicyclopentyl-1,3-dimethoxypropane, 9,9-bis(methoxymethyl)fluorene, diisoamylether, sec-butylether, tetrahydrofuranne and dioxane. It is also possible to employ any mixture of the above compounds.
The first and second electron donors are preferably aliphatic or cyclic ethers, notably diusoamylic ether, sec-butylether or tetrahydrofuranne. Particularly preferred are the aliphatic ethers.
In order to excercise strict control of the morphology of the final support, it is preferred to associate the components with each other in appropriate amounts. Thus, the Mg/Al molar ratio is comprised between 5 and 200, preferably between 10 and 80. Chlorine-containing organic compound concentration is such that the Cl/Mg molar ratio is preferably above 2, advantageously it is comprised between 2 and 4. The amount of second electron donor to be implemented with the alkylmagnesien derivative and the aluminum organic compound is such that the molar ratio of the second electron donor to the magnesium is comprised, preferably, between 0.01 and 5. The amount of first electron donor to be implemented with the chlorine-containing agent is such that the molar ratio of this first electron donor to magnesium is comprised, preferably, between 0.01 and 5.
In the framework of this invention, the support such as described above is treated, in suspension in an inert solvent, by an activating electron donor. The molar ratio between activation electron donor and magnesium initially introduced is generally comprised between 0.1 and 3. To avoid any deterioration of the magnesium chloride-based support, it is desirable for the activation electron donor to be highly diluted in the inert liquid. The volume ratio between the inert liquid and activation donor is generally comprised between 1 and 20, preferably between 1 and 10. This treatment can be done with stirring at a temperature comprised between 20xc2x0 C. and (Teb+20xc2x0 C.). Teb being the boiling point of the activation electron donor. Preferably., this temperature is comprised between 20xc2x0 C. and (Tebxe2x88x9210xc2x0 C.). In this range of preferred temperatures, the support and catalyst are more solid and less fines (with span elevation) are produced during polymerization. The activation electron donor is preferably a cyclic ether selected from the monoethers the oxygen of which forms a cycle having at least 4 and at the most 12 carbon atoms. It is not excluded for some of the carbon atoms of the cycle to be bound to substituant hydrocarbon radicals, the total number of carbon atoms of the cyclic ether not exceeding, in this case, 16. Among these ethers, the following can be cited: tetrahydrofuranne, tetrahydropyrane, 2-methyl-tetrahydrofuranne, 3-methyl-tetrahydropyrane; tetrahydrofuranne being preferred.
The supports according to the invention are particularly suitable for producing Ziegler-Natta catalysts for olefin polymerization, based on halides of group IV transition metal such as titanium.
The support is for example impregnated with transition metal halide, more particularly of formula Ti(OR)nX4-n where R is an alkyl radical with 1-12 carbon atoms, X is a halogen and n is an integer comprised between 0 and 4, preferably TiCl4. Impregnation can be done conventionally by adding a sufficient amount of transition metal halide to the support, optionally in an inert solvent to form a homogeneous suspension. Such impregnation can be done in the presence of an electron donor. The support can optionally undergo two or more successive impregnations with the compound of general formula Ti(OR)nX4-n, wherein each impregnation may or may not be carried out in the presence of an (impregnation) electron donor.
The invention also provides a process for preparing a catalyst.
The impregnation electron donors suitable for the preparation of supported catalysts are organic compounds comprising one or several oxygen, nitrogen, sulfur or phosphorus atoms. By way of example we can cite organic acids, organic acid esters, alcohols, ethers, aldehydes, ketons, amines, amine oxides, amides, thiols. The association of one or several of the above electron donors can be implemented. More specifically, the currently employed electron donors containing one or several oxygen atoms can be organic acid esters or ethers. More specifically, these can be mono- or dicarboxylic aromatic esters or diethers. Examples of aromatic esters are the dialkylphtalates wherein the alkyl group contains 1-20 carbon atoms, preferably 1 to 10 carbon atoms, such as di(n-butyl)phtalate, diisobutylphtalate, dioctylphtalate, diheptylphtalate, diethylphtalate. The following examples of diethers can be cited: 2,2-diisobutyl-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-diethoxypropane, 2-isopropyl-2-isobutyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclolhexyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane, 2,2-dicyclopentyl-1,3-dimethoxypropane, 9,9-bis(methoxymethyl)fluorene.
The amount of impregnation electron donor can vary. With advantage, it is comprised between 2 and 20% and preferably between 4 and 16% by weight of the catalytic component.
According to one embodiment, the amount of impregnation electron donor is less than 9% by weight of the catalytic component. According to this embodiment, the production of polyalphaolefin having a widened molecular weight distribution is favored.
According to another embodiment, the amount of impregnation electron donor is greater than 9% by weight of the catalytic compound. In this embodiment, a supported catalyst is obtained having very high productivity. Suitable inert solvent for the synthesis of Ziegler-Natta catalyst are the aliphatic hydrocarbons such as hexane, heptane or decane, alicyclic hydrocarbons such as cyclohexane or ethylcyclohexane, aromatic hydrocarbons such as toluene, xylene or chlorobenzene or any mixture of the above solvents.
The catalytic component thus prepared is associated with a co-catalytic system for providing olefin polymerization. This cocatalytic system is constituted by a cocatalyst and, optionally, an electron donor. The cocatalyst is generally chosen from group III metal alkyls. Among these products we can mention: the alkylaluminiums such as trimethylaluminium, triethylaluminium, trilsobutylaluminium and combinations thereof. The cocatalytic electron donor can be selected from the aliphatic or aromatic silanes of general formula SiR4 wherein R can be an alkyl group containing 1 to 20 carbon atoms and/or an alkoxy, ORxe2x80x2 group, Rxe2x80x2 being an alkyl group containing 1 to 20 carbon atoms. The cocatalytic electron donor can also be chosen from the family of silacycloalkanes. The cocatalytic electron donor can also be chosen from the family of diethers of general formula R1R2C(CH20R3)2, R1, R2 and R3 can be alkyl groups containing 1 to 20 carbon atoms. As cocatalytic electron donor, one for example will prefer dicyclopentyl dimethoxysilane, cyclohexylmetlhyldimethoxy-silane, diisobutyldimllethoxysilane.
The invention applies to polymerization of xcex1-olefins and more particularly propylene, as well as copolymerization or terpolymerization of xcex1-olefins. In the case of copolymerization, the other monomer can be ethylene or another monomer. When the comonomer is not an xcex1-olefin, it makes up less than 50% by weight. The term xcex1-olefin such as employed in this specification covers olefins comprising 3 to 20 carbon atoms, preferably 3 to 8 carbon atoms. The preferred xcex1-olefin is propylene. In the case of copolymers of propylene, for example with ethylene or butene, the comonomer generally makes up less than 300% by weight. In addition to the stereospecific polymers which may be made using the catalyst of the invention, the catalyst also makes it possible to provide, with high productivity, non stereospecific polymers such as random copolymers of xcex1-olefins having a high ratio of a comonomer such as ethylene.
The xcex1-olefin polymerization can be done using known processes, in solution, in suspension, bulk or in the gas phase.
Preferably, the mean diameter of the catalyst according to the invention is comprised between 5 and 50 xcexcm when used with a suspension process and between 20 and 150 xcexcm when used with a gas phase process.
A chain transfer agent can be employed for controlling melt index of the polymer to be produced. The chain transfer agent can be hydrogen introduced in an amount of up to 90% and generally in the range 0.01 to 60 mole-% of the total olefin and hydrogen introduced in the reactor. This chain transfer agent makes it possible to obtain a given melt index, knowing that the melt index increases when the amount of chain transfer agent increases. The invention offers the advantage of causing little chain transfer agent to be consumed for a given melt index.
The invention also provides a process for xcex1-olefin polymerization comprising the following steps:
(i) preparation of a support as described above;
(ii) activation of the support as described above;
(iii) preparation of a catalyst on the activated support of step (ii), as described above;
(iv) contacting an xcex1-olefin charge with the catalyst under polymerization conditions.